In Institute of Electrical and Electronics Engineers, IEEE, Wi-Fi (also known as Wireless Local Area Network, WLAN, and these terms will be used interchangeably throughout this document) is standardised in the 802.11 specifications (IEEE Standard for Information technology—Tele-communications and information exchange between systems. Local and metropolitan area networks—Specific requirements. Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications). Wi-Fi is a technology that currently mainly operates on the 2.4 GHz or the 5 GHz band. The IEEE 802.11 specifications regulate the access points' or wireless terminals' physical layer, MAC layer and other aspects to secure compatibility and inter-operability between access points and portable terminals. Wi-Fi is generally operated in unlicensed bands, and as such, communication over Wi-Fi may be subject to interference sources from any number of both known and unknown devices. Wi-Fi is commonly used as wireless extensions to fixed broadband access, e.g. in domestic environments and hotspots, like airports, train stations and restaurants.
The WLAN technology relies on Carrier Sensing Multiple Access with Collision Avoidance, CSMA/CA, in order to effectively and fairly share the wireless medium among different WLAN entities and even different Radio Access Technologies, RAT. CSMA/CA applied by the WLAN system demands that every device that wishes to send data senses the common communication channel before carrying a transmission in order to avoid duplicate transmissions (usually resulting in loss of data and need of retransmissions). In order for a device to deem the channel busy, it has to detect a transmission, the received signal strength level of which surpasses a pre-determined threshold, referred to as the Clear Channel Assessment, CCA, threshold, CCAT.
A problem may be that an AP or wireless device may refrain from accessing the medium since it is exposed to concurrent transmissions in neighbouring Basic Service Sets, BSSs, although simultaneous communication would be possible. This limits the performance of current systems, especially as the CCA threshold used today is very low, −82 dBm.
In the past, WLANs were mainly used to transport low-bandwidth, data-application traffic. Currently, with the expansion of WLANs into vertical (such as retail, finance, and education) and enterprise environments, WLANs are used to transport high-bandwidth data applications, in conjunction with time-sensitive multimedia applications. Consequently, the load of the WLANs has increased substantially during the last years and is likely to increase even further. With increased traffic, denser WLANs, the interference may increase and it may reduce the probability of an AP and/or a wireless device to swiftly access a channel or radio resources of the WLAN.